From the introduction:
So you have purchased the Psionics Handbooks, and one of your players has decided to use a psionic class. You want psionics to be part of your world. The problem is that you use a lot of pre-made modules, and those don’t include a lot of psionic characters. Or maybe you’ve procrastinated finishing tonight’s adventure. You’ve got the caverns mapped out, and the traps set, you just don’t have the statistics of the main villain. Or maybe you are looking for a few new ideas to spark you imagination. You might want a reoccurring villain to challenge your characters over the course of the campaign, or you might just need a one short conflict for next week game.
Whatever your needs, if you use psionics and you use NPCs, this book is for you. NPCyclopedia: Psionics features eleven different psionic NPCs. Each contains a detailed background, adventure hooks, combat tactics, and statistics for every level from 1 to 20. A complex interconnected background between all characters allows you to use these as both one shot NPCs at any level of your choice instantly, or even as interconnected NPCs spanning a longer campaign.